In general, nitrogen oxides (NOx) are produced when oxygen and nitrogen are combined at high pressure and high temperature, and in order to suppress the combination, an EGR (exhaust gas recirculation) system that reduces production of NOx by reducing the highest combustion temperature and reducing supply of oxygen by supplying some of exhaust gas discharged to the atmosphere back to an intake port is used.
When some of the exhaust gas discharged to the atmosphere is supplied back to the intake port, the combustion status of fuel depends on the amount of combustion gas supplied back to the intake port by the EGR system, which influences the power of an engine and NOx and PMs (particulate matter) contained in the exhaust gas. That is, the EGR system decreases the combustion temperature of the engine and reduces the production amount of NOx by returning some of the exhaust gas discharged from the engine to the intake system of cylinders.
As described above, in an EGR system, the amount of exhaust gas that is returned is an important factor and the part that controls the gas that is returned is an EGR valve. The EGR valve is disposed in a recirculation channel to be able to control recirculation of exhaust gas and can sense the height of a shaft coupled to the valve, that is, a valve shaft.
An EGR valve in the related art is described hereafter in detail with reference to the accompanying drawings.
FIG. 1 is a perspective view showing the internal structure of an EGR valve of the related art and FIG. 2 is a partial cross-sectional view of the EGR valve of the related art.
As shown in FIGS. 1 and 2, the EGR valve of the related art includes: a valve shaft 10 vertically disposed and moving up and down by rotating about its vertical central axis; a cylindrical cam 30 integrally fitted on a portion of the valve shaft 10 and having a spiral groove 32 on the outer side and a polyhedron 34 at the upper end; a fixed bearing 50 fixed to a side of the cylindrical cam 30 with one end slidably inserted in the spiral groove 32; a rotary gear 40 having the polyhedron 34 inserted on the rotational axis therein; a cylindrical magnet 20 coupled to the upper end of the valve shaft 10 passing through the cylindrical cam 30; a hall sensor 60 fixed to a side of the cylindrical magnet 20 and sensing up-down movement of the cylindrical magnet 20; and a return spring 80 returning the rotational angle of the rotary gear 40 to the initial state.
When the rotary gear is rotated by a separate rotary motor, the cylindrical cam 30 and the valve shaft 10 are rotated with the rotary gear 40, and in this process, the position of the spiral groove 32 in which the fixed bearing 50 is inserted is changed, so the cylindrical cam 30 and the valve shaft 10 move upward along the slope of the spiral groove 32 while rotating. As the valve shaft 10 moves up by rotating, the cylindrical magnet 20 also moves up by rotating and the hall sensor 60 senses the upward movement of the cylindrical magnet 20 and can calculate the upward movement distance of the valve shaft 10.
Meanwhile, as the valve shaft 10 rotates while moving up, the cylindrical magnet 20 at the end of the valve shaft 10 also rotates, in which when the magnet is not precisely magnetized, the magnetic flux may be changed by the rotation. When the magnet flux is changed, as described above, the hall sensor 60 may generate a sensing error, that is, it may sense the change as a vertical position change of the cylindrical magnet 20. Further, as the rotary gear 40 is rotated, the return spring 80 is rolled and the diameter decreases, so the side of a housing interferes with the return spring 80. Meanwhile, generally, the rotary gear 40 is made of synthetic resin and the housing 70 is made of an aluminum alloy, so when the rotary gear 40 and the housing 70 are brought in direct contact with each other, they may be damaged due to friction between different materials.